Patent GB-478569-A (GB)
Title: Improvements relating to machines for machining propeller-blades
IPC: B23Q35/10
Filed: 1936-07-15
Abstract: 478,569. Machining propeller-blades. STONE & CO., Ltd., J., and LYTH, C. J. July 15, 1936, No. 19638. [Class 83 (iii)] [Also in Groups XXIII and XXIX] In a machine for producing propeller-blades, wherein means are provided for producing a basic relative movement between the tool and the blade such that the tool generates a helicoidal surface relative to the blade, a servomotor is provided to impart to the tool additional movement parallel to the axis of the propeller, and a controlling cam the contour of which varies with the length, to impart to the blade a required departure from the helicoidal surface. The main guide 1 supporting the tool and extending over the propeller table 2, is carried by a vertically-moving saddle 3 on a column 4. The main guide can be angularly adjusted about the axis 5. The saddle 3 is counterbalanced by a weight 8, Fig. 2. The movement of the table and saddle are connected in such a way that the tool on the blade generates a helicoidal surface. The guide 1 carries a second horizon tally-movable saddle 10, Fig. 1, moved by a feed screw 11. A tool-carrying assembly is movable vertically in a frame 13 adjustably secured by studs 14 and arcuate slots to the saddle 10. The frame 13 carries a horizontal guide 131 which engages a frame 16 steadied by the vertical shaft 17. The tool-carrying assembly comprises a milling head 20, a vertical slide 18, an electric motor 19, and a hydraulic control gear. The tool cut may be varied by a screw 23. The frame 13 carries a bracket 25 supporting a hydraulic cylinder 26. The piston-rod is fixed to a bracket 28. The liquid is controlled by a valve 29 operated by a cam 34. The cylinder and valve-chest are provided with hydraulic connections 30. The hydraulic cylinder may be single-acting with admission of pressure fluid to the lower end only of the cylinder 26. In order that gravity need not be relied on to overcome frictional resistance to downward movement, an auxiliary admission of low-pressure fluid may be made to the upper end of the cylinder 26 in known manner. The admission and exhaust of low-pressure fluid takes place with the exhaust and admission of high-pressure fluid respectively. The cam is mounted on a shaft 36 operated by toothed gearing 38, 39. The cam takes account only of divergencies of contours from a given helicoidal surface. The circumferential contour at any point corresponds to the varying divergence from the helicoidal surface of the required blade contour at the corresponding arcuate section of the blade. The cam and table are kept in phase by driving them from the same shaft. The cam consists of thin, accurately-shaped, cam-plates 43 spaced by cement, plaster, &c. 45 which is formed to an easy and continuous surface. The cam may be rotated two or three times as fast as the propeller if a 1 : ratio gives a too-large cam slope. The main drive shaft 75 drives by bevel-gearing a shaft 77 which drives the feed screw 79 to operate the saddle 3. The shaft 77 drives through gearing 80 and a reversing-gear box 81 a shaft 82 to drive the table 2 through worm-gearing 83, 84. Shaft 17 is driven by a non-reversible shaft 85 through worm-gearing 86. Since the table drive can be reversed, the same can be employed for generating similar blades by right and left hand screws. If the pitch of the blade varies from the root to the tip the gearing 80 is selected to suit an intermediate pitch valve and the divergence is rectified by the cam. The same effect could be secured with a fixed valve-housing by an arrangement shown in Fig. 4. The lever 47 actuated by the cam 34 is connected to a valve 46, and to a lever 48 connected to the slide 18. When the slide is moved hydraulically it restores the valve 46. With steep sloped cams, the valve may be operated by means which respond to transverse as well as to vertical movements of the tracer means. A rod 50, Fig. 5, with a middle ball 53 and end balls 51, 52 is arranged to operate admission and exhaust lift valves 62, 63. The cam-engaging ball 51 runs on a ring of balls 51<1>. The ball 52 engages a conical recess 55 in a spring-pressed rod 57 provided with a valve-actuating head 64. The spring-pressed bearing 54 is guided in a yoke 58. Small rockers may be used instead of the head 64. Instead of imparting an additional movement to the slide and tool-carrying assembly, it may be superimposed on the drive of the saddle 3. A differential gearing 69, Fig. 6, is introduced between the driving and driven shafts 70, 71. The casing of the gearing may be controlled by a rack-and-pinion and a hydraulic cylinder 74 whose valve is controlled by a cam similar to 34. When the invention is applied to a machine in which the blade is planed or shaped, the milling cutter is replaced by a single-point tool in a clapper box carried on the slide 18. The saddle 10, slide 18 and tool would be reciprocated radially towards and away from the axis of the propeller, the tool cutting towards the axis. The screw would be driven by a reversing motor, or a Whitworth quick-return movement may be used. The movement of the blade would take place at the end of each reciprocation. The cam follower would move along the cam parallel thereto, the cam being rotated with the table. Specification 167,664, [Class 83 (iii)], is referred to.